The present invention relates to the papermaking arts including fabrics and belts used in the forming, pressing, and drying sections of a paper machine, and to industrial process fabrics and belts, TAD fabrics, engineered fabrics and belts, along with corrugator belts generally.
The fabrics and belts referred to herein may include those also used in the production of, among other things, wetlaid products such as paper and paper board, and sanitary tissue and towel products made by through-air drying processes; corrugator belts used to manufacture corrugated paper board and engineered fabrics used in the production of wetlaid and drylaid pulp; in processes related to papermaking such as those using sludge filters and chemiwashers; and in the production of nonwovens produced by hydroentangling (wet process), meltblowing, spunbonding, airlaid or needle punching. Such fabrics and belts include, but are not limited to: embossing, conveying, and support fabrics and belts used in processes for producing nonwovens; filtration fabrics and filtration cloths; and fabrics and belts used for textile finishing processes such as calendering and hide tanning.
Such belts and fabrics are subject to a wide variety of conditions for which functional characteristics need to be accounted. For example, during the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
It should be appreciated that these industrial fabrics such as paper machine clothing (PMC) such as the forming fabrics, press fabrics, and dryer fabrics, all take the form of endless loops on the paper machine and function in the manner of conveyers.
Such fabric structures are typically constructed from synthetic fibers and monofilaments by conventional textile processing methods such as weaving, for example. It is often desirable to selectively tailor the fabric structure to affect or enhance a performance characteristic important to, for example, the papermaker, such as fabric life, sheet formation, runnability or paper properties.
For fabrics such as those used for the forming of paper and tissue products, or for the production of tissue/towel or through-air drying “TAD” fabrics, such fabrics are often times joined by a seam. In this instance, the fabric is usually flat woven from yarns, usually monofilaments. Each fabric edge has a “fringe” of machine direction (“MD”) yarns. This fringe is rewoven with cross machine direction (“CD”) yarns in the same basic pattern as the fabric body. This process of seaming to make endless is known to those skilled in the art. The seam area therefore contains MD yarn ends. The strength of the seam is dependent upon the MD yarn strength, the number of MD and CD yarns used, and the crimp in the MD yarns themselves that physically “lock” themselves around CD yarns to an extent. However, when the fabric is under operating tension on, for example, a papermaking or tissue/towel making machine, these MD yarn ends can literally slip past one another and pull out. The “ends” themselves can protrude above the fabric plane causing small holes in the paper/tissue product or can eventually slip enough so that ultimately, the fabric seam fails and the fabric pulls apart. Typically, the width of the seam area, as measure in MD, formed using conventional techniques range, for example, anywhere between three and one half to twenty inches or even more.
To minimize this, the yarns in the seam are usually sprayed or coated with an adhesive. Unfortunately, this can alter the fluid handling properties of the seam area, and the adhesive can also be abraded and wear off.
While the application of heat to partially weld or fuse yarns to each other in the seam area has been contemplated, the use of heat generally may cause unacceptable change to the fluid handling properties of the seam area since all yarns are affected and the seam may, for example, have a resultant air permeability different than the fabric body.
Other shortcomings of the prior attempts are that either because of the number of yarns used in the MD, or the size of the yarns used, sufficient seam strength cannot be obtained by conventional seaming methods, even with the additional use of glues/adhesives.
It is known in the paper machine clothing and/or industrial fabric arts to utilize thermal energy to fuse yarns together to form a seam in for example, a flat woven fabric of machine direction (MD) and cross machine (CD) yarns.
The need to maintain yarn properties as well as fabric properties in the seam area is paramount. Yarns used in PMC and other industrial fabrics are made from oriented polymers such as polyester, and have a desired shape and size. It is necessary to maintain essentially the yarn size, shape and characteristics after application of thermal energy. However, heat can affect these materials in a variety of adverse ways. For example, heat can cause (a) softening above the glass transition point of a thermoplastic material which effects dimensional changes, or (b) flow by melting above the melt transition point.
Seam openness should be maintained by not causing major distortion of the yarns in the seam area. Also, high yarn tensile strength, especially in the MD yarns should be maintained or resultant seam strength will be unacceptable.
While some “melt flow” is required to have at least portions of two adjacent yarns bond to each other and/or bond to CD yarns that they crossover, no major distortion of the yarn should occur. So there is a need to balance the desired yarn, seam and fabric properties compared to the amount and location of the absorbed thermal energy as exemplified in FIG. 1.
Thermal welding of polymers is achieved by either overlapping of the two MD yarns, for example, to be welded together by some distance, or end to end welding of two yarns, or either of these in conjunction with fusion to a yarn oriented in another direction in the fabric, for example, at least one CD yarn. Welding can also occur with just one MD yarn welded to a CD yarn at a crossover.
There have been attempts to use lasers to weld thermoplastic materials together, but “weld quality” and over-fusing of the material was suspect. Such “over-fusing” would be unacceptable for the yarns used in the fabric applications envisioned.
Laser technology has advanced, producing laser types that would better control and focus the thermal energy.
A further development based upon the principles of transmission (some laser wavelengths are transparent to polymeric materials, such as polyester for example polyethylene terephthalate (PET) and polyamide (PA)) and absorption is to use a radiation absorbing material within a polymer matrix or applying it to for example, a polymeric yarn surface in a discrete location where thermal fusion or welding is desired. US Patent Application US2004/0056006A1 assigned to The Welding Institute, exemplifies such technology. However, nothing in this application addresses the needs of using a similar approach on adjacent yarns for example in the seam of a forming or other industrial fabric.
Another example of using laser energy and an energy absorbing material is taught in PCT Application WO02/057353A2 assigned to EI Dupont De Numours and Company. Again however, the teachings are for bonding materials shaped by injection molding and do not address the requirements of producing fabrics and improved seams in such fabrics when using oriented polymeric yarns.
Canadian patent application 2,552,009, assigned to Heimbach GMBH & Co., KG relates to a forming fabric for use in a sheet forming section of a papermachine, having or comprising a textile planar structure in which, in order to enhance inherent stability, intersecting yarns are engaged into one another at intersection points and in which yarns additionally are fused to one another, which is characterized in that the planar structure comprises intersecting first and second yarns, the first yarns having the property that they absorb laser energy and can be brought by absorbed laser energy, to melting temperatures at least at the surface; and that first and second yarns are fused to one another at least at some of their intersection points.
The application teaches that one of the two yarns contains a laser energy absorbing material. Further, when addressing the seam area of a woven fabric, the application teaches that in the seam region, first yarns (that contain the laser energy absorbing material) should be present that extend in the transverse direction and are welded to second yarns extending in the longitudinal direction. In order to achieve particularly high seam strength there, the first yarns should be present in a higher concentration in the seam region than in the remaining region of the forming fabric, and the first and second fabrics (sic) should be welded to one another at as many intersection points as possible. The longitudinal yarns inserted in correctly woven fashion into the respectively opposite end during the stitching process are then fused to the first yarns. This creates the possibility of shortening the seam region without thereby impairing the strength of the seam. In this fashion the seam region can be reduced from a usual extension of, for example, 100 mm in the longitudinal region to, for example, 60 mm, i.e. the seam region can be shortened by 20-60% in the machine direction.
However, an apparent major shortcoming of this approach is that the other properties of the seam such as its permeability, number of sheet support points, and Fiber Support Index (FSI) will be different from the main fabric body as the end counts in the CD will be different.
Thus, the fusing or welding of synthetic polymeric yarns by focused laser energy, especially those in the seam area of woven fabrics, without causing appreciable loss of yarn properties; major alteration of size and/or shape of the yarns; having a seam that has properties like the body of the fabric; that the seam has, if the seam is the same length in the MD as normally used, higher durability, and strength equal to or higher than an unfused or unwelded seam; and if the seam is shorter in the MD than normally used, strength sufficient to allow the fabric to run a useful life when installed and used on a paper or other industrial machine, is the subject of the present invention.